Plastic Separation Module

ABSTRACT

An automated system for sorting dissimilar materials, and in particular for sorting plastics from other materials and for sorting different types of plastics from one another comprises, depending upon the embodiment, combinations of a sizing mechanism, a friction separation, an air separator, a magnetic separator, a dielectric sensor sortation bed, shaker screening, a ballistic separator, an inductive sensor sortation system and a float/sink tank. The dielectric sensor sortation system may be either analog or digital, depending upon the particular implementation. One or more float/sink tanks can be used, depending upon the embodiment, each with a media of a different specific gravity. The media may be water, or water plus a compound such as calcium chloride. In addition, multiples of the same general type of module can be used for particular configurations. A heavy media system or a sand float process can be used either alternatively or additionally.

RELATED PATENT APPLICATIONS

This non-provisional patent application is a divisional of U.S. patentapplication Ser. No. 11/586,309, entitled “Dissimilar Materials SortingProcess, System and Apparata,” filed on Oct. 24, 2006, which claimspriority under 35 U.S.C. §119 to U.S. Provisional Patent ApplicationNos. 60/777,868, entitled “Method and Apparatus for Sporting,” filed onMar. 1, 2006, and 60/729,966, entitled “Method and Apparatus for SortingDissimilar Materials,” filed on Oct. 24, 2005, as well as priority under35 U.S.C. §120 to: (a) U.S. patent application Ser. No. 11/255,850,entitled “Method and Apparatus for Sorting Metal,” filed on Oct. 21,2005, which claims priority under 35 U.S.C. §119 to U.S. ProvisionalPatent Application No. 60/621,125, entitled “Method and Apparatus forSorting Metal Pieces,” filed on Oct. 21, 2004; and (b) U.S. patentapplication Ser. No. 11/584,196, entitled “Method and Apparatus forSorting Contaminated Glass,” filed on Oct. 20, 2006, which claimspriority under 35 U.S.C. §119 to U.S. Provisional Patent Application No.60/728,581, entitled “Method and Apparatus for Sorting ContaminatedGlass,” filed on Oct. 20, 2005. Each of the foregoing priority andrelated applications is hereby fully incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to materials sorting processesand systems, and more particularly relates to processes, systems,apparata and techniques for sorting dissimilar materials such as for thepurpose of recycling some or all of such materials.

BACKGROUND

Recycling of waste materials is highly desirable from many viewpoints,not the least of which are financial and ecological. Properly sortedrecyclable materials can often be sold for significant revenue. Many ofthe more valuable recyclable materials do not biodegrade within a shortperiod, and so their recycling significantly reduces the strain on locallandfills.

However, in many instances there has been no cost-effective method forachieving the necessary sorting. This has been particularly true for,for example, non-ferrous materials, and particularly for non-metallicssuch as high density plastics. For example, one approach to recyclingplastics has been to station a number of laborers along a sorting line,each of whom manually sorts through shredded waste and manually selectsthe desired recyclables from the sorting line. This approach is notsustainable in most economics since the labor component is too high.

While ferrous recycling has been automated for some time, mainly throughthe use of magnets, this technique plainly is ineffective for sortingnon-ferrous materials.

As a result, there has been a need for a cost-effective, efficientprocess, system and apparata for sorting dissimilar materials, includingplastics, in a manner which facilitates significant revenue recoverywhile also significantly reducing landfill.

SUMMARY

Recyclable wood, rubber, metal, wire and plastics account for asignificant share of the solid waste generated. It is highly desirableto avoid disposing of wood, rubber, metal, wire and plastics in alandfill, and instead to recycle these materials. In order to recycledifferent materials from a mixed waste, the wood, rubber, metal, wireand plastics must be identified and separated. The present inventionprovides a process, for sorting, without human intervention, dissimilarmaterials such as wood, rubber, metal, wire and plastics, from a groupof mixed materials where, in at least some arrangements, each suchmaterial may appear at random times or in random quantities within themix. In addition, the present invention provides a system for executingthe process, and also provides novel apparata for performing certain ofthe steps of the process. The exemplary arrangements discussedhereinafter include a variety of steps, or a variety of modules, and notall steps or all modules need be implemented in every embodiment of theinvention. Likewise, the sequence in which various of the process stepsare executed can be varied in appropriate circumstances withoutdeparting from the invention.

In one arrangement, the process comprises a sequence of sorting stepsfor extracting from a mixed material stream a component of that stream,or a group of related components. As each component or group is removed,the residue is passed to the next step for further processing. Once eachpreliminary component is removed, the remaining residue is also adesired component or group.

The system of the present invention includes a plurality of modules orstages, where each stage typically performs a different sortingfunction, with the result that different materials are separated out ofthe mix at different times, until finally each type of recyclable hasbeen sorted out of the mix and the residue—now typically substantiallysmaller in volume than the original mix—may be routed for otherprocessing or discarded.

Depending upon the particular implementation, the system of the presentinvention includes a plurality, though not necessarily all, of a groupof apparata comprising a magnetic separator, a friction separator whichmay, for example, be a rollback friction separator, a dielectric sensorsortation bed, shaker screening, a ballistic separator, and an inductivesensor sortation system. The dielectric sensor sortation system may beeither analog or digital, depending upon the particular implementation.An air separation module may also be provided, which may include an airknife or other system which uses air to separate a lighter fraction froma heavier fraction. In addition, multiples of the same general type ofmodule may be used, although the specific configuration of each suchmodule may be optimized to select somewhat different elements of themix. One or more float/sink tanks may also be implemented, by which toseparate less dense materials from more dense materials, and thespecific gravity of the tank media may be adjusted for each tank topermit selection of the materials intended to float versus thoseintended to sink. For some float/sink tanks, the media may be water, orwater plus an additional compound, depending upon the particularmaterials to be sorted and the volumes to be handled. Alternatively, aheavy media plant can be used. If a dry process is preferred, a sandfloat tank can be used.

Depending upon the implementation, various types of dielectric sensorsand sensor array configurations can be used in the inventive sortingsystem. Typically, each of the sensor arrays includes a number ofproximity sensors placed in a pattern across the path of the mixedmaterials. The sensors can be analog or digital, shielded or unshielded,capacitive or inductive proximity sensors. Each type of sensor hasspecific material detection characteristics and in turn generatedifferent signals when metal, glass, plastic, wood or rubber pieces aredetected, as discussed in more detail hereinafter.

In addition, where the sorting process may be aided by ensuring asuitable moisture content, a mister or humidifier may be included in theappropriate module. While adding moisture can be helpful in some stepsof the sorting process, particularly with regard to increasing thedielectric constant of absorbent materials, in other sorting steps ofsome embodiments an IR heat source of sufficient BTU's to ‘flash’ drythe materials can provide better uniformity of operation, the details ofwhich are discussed hereinafter. Still further, in some sorting stepsfor certain embodiments, for example where dielectric sensors are used,the use of temperature and humidity control around the sensors canprovide improved uniformity of operation.

In addition, multiple groups of modules may be configured as multiplesorting lines, for example to sort different sizes of materials. In onesuch arrangement, a first sorting line may sort material over apredetermined size, while another sorting line may sort material lessthan that predetermined size. The number of such sorting lines is notlimited, and may be matched to the volume of the mix, and the type ofmix, which is desired to be sorted.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A shows a process flow diagrams of an implementation of theprocess of the present invention.

FIG. 1B shows a process flow diagram of an implementation of the processof the invention particularly suited to recovery of wire and metals, andshows the alternatives of a float/sink tank, a heavy media system, or adry sand float process.

FIGS. 2A-2C, taken together, show in side elevational view a system inaccordance with the present invention.

FIGS. 3A-3B show, in side elevational view and in top plan view,respectively, a magnetic sorting module in accordance with the presentinvention.

FIGS. 4A-4B show, in side elevational view and in top plan view,respectively, a rollback friction separator module in accordance withthe present invention.

FIG. 5 shows in side elevational view a low pass dielectric sensormodule in accordance with the present invention.

FIGS. 6A-6D show examples of alternative arrangements of proximitysensors for use with the inductive and dielectric sorting modules of thepresent invention, including arrangements which offer reduced crosstalk.

FIGS. 7A-7B illustrate in greater detail a ballistic separator module inaccordance with the present invention.

FIG. 8 illustrates in side elevational view an inductive sensing modulein accordance with the present invention.

FIG. 9 illustrates in side elevational view a bandwidth dielectricsorting module in accordance with the present invention.

FIG. 10 illustrates an implementation of a float/sink tank in accordancewith the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Referring first to FIG. 1A, an aspect of the process of the presentinvention, indicated generally at 100, may be better appreciated. Asindicated at step 105, an incoming stream of mixed material typicallyincludes wood, rubber, ferrous and non-ferrous metals, wire includinginsulated wire coated with a plastic cover, and a variety of types ofplastic pieces, including foam, polyethylene, polystyrene, ABS, and soon.

In the illustrated embodiment, the process proceeds at step 110 byseparating out the magnetic materials, which typically includes theferrous metals such as iron and steel, as well as certain ceramics. Inmost instances, the valuable magnetic materials have already beenremoved from the stream, and so the magnetic materials remaining at thisstage is mostly waste. These materials are diverted for furtherprocessing as required by the particular implementation, as shown at115. For many streams, the further processing may be nothing more thandisposal, although this will depend on the particular implementation andwaste stream being sorted. An air system can also be used at this stage,either as an addition to the existing module or, in some embodiments, asa replacement. The air system comprises either an air knife or otherarrangement for separating heavier and lighter fractions using blowingair. The resulting concentrated fractions will comprise, for the heavierside, wire and metals, rubbers, wood, and possibly some other densematerials including perhaps some dirt. The lighter concentrate willcomprise primarily plastics, paper, some foam, and possibly other lightmaterials.

Following the removal of the magnetic materials, the process advances tostep 120, where light or round materials, such as foam and rocks, arediverted for further processing, as indicated at step 125. Again, insome instances such processing may be merely disposal.

Next, as indicated at step 127, alternative process steps 130 and 140exist depending upon the composition of the mixed material stream. Ingeneral, although not required, it is desirable to continue processingthe majority fraction of the stream, and to select the minority fractionfor diversion to other processing. This can be achieved by selectionbased on dielectric constant, since most plastics valuable for recyclinghave dielectric constants on the order of 3 or less, while the othermaterials typically have higher dielectric constants, particularly wetmaterials that are absorbent, rubbers, and so on and discussed in moredetail later.

Thus, if the materials stream has plastics as its minority fraction,then materials having a dielectric constant below a certain thresholdare diverted for further processing as shown at step 135. Thesematerials typically include, for example, polypropylene andpolyethylene, polystyrene and ABS, as well as some waste materials. Thematerials having a higher dielectric typically comprise wet or moistwood, foam, rubber, and so on. In one embodiment, the threshold for alow dielectric constant can be on the order of 3.0 although the preciseset point can vary significantly depending upon the materials.

Alternatively, as indicated at step 140, if the majority fraction isplastics, then materials having a dielectric constant above apredetermined threshold are separated out and diverted for furtherprocessing, as shown at step 145. These materials include differentforms of wood, rubber, foam and so on. In one embodiment, the thresholdfor a high dielectric constant may be on the order of 3.4. It will beappreciated that, at this point, the remaining materials are only thosewhich have are non-magnetic, suitably dense, and having a dielectricconstant below a specified threshold (or, for analog sensors, aspecified range), plus a very small amount of other waste. The vastmajority of this concentrate typically comprises recyclable polymers,i.e., plastics, having a relatively high value in the recycling marketsuch as polystyrene and ABS, plus other less dense plastics.

However, other materials, typically among those diverted at steps 135and 145, may also represent significant value as raw recyclablematerials. To recover these, additional processing steps can be used. Asindicated at step 155, a density separation step may be used wheredenser materials, such as wire, are separated out from lower densitymaterials such as wood and rubber by the use of a float/sink tank, heavymedia process, or sand float process as discussed hereinafter,particularly in connection with FIG. 1B and FIG. 10. The wire can thenbe collected for further processing as shown at step 160. The residue ofwood, rubber and any other materials from steps 145 and 155 can then besorted optically, as shown at step 165, such that the rubber iscollected as shown at step 170, and the wood is collected as shown atstep 175. It will be appreciated by those skilled in the art that noteach of the foregoing steps will be required for every implementation ofthe inventive process, since variations may occur in the materials mixor in the economic benefit of recycling certain of the materials, inwhich cases those processing steps may be removed from the process.

Next referring to FIG. 1B, a process for reclaiming recyclable wire fromthe materials stream may be better appreciated. It will be appreciatedthat the process of FIG. 1B can be integrated into the embodiment shownin FIG. 1A, or can be run separately, depending upon the nature of thematerials stream and the decision as to which materials should berecovered. For convenience, the major steps in the wire recovery processare shown in FIG. 1B. The materials stream is provided at step 105, asin FIG. 1A, where the materials typically have been screened to ensure arelatively uniform size, although such screening is not critical in allembodiments. The magnetic materials are then separated as shown at 110,followed by a separation of the remaining stream into heavy and lightfractions as shown at step 175.

The separation into heavy and light fractions can be accomplished inseveral ways, for example by a ballistic conveyor with an air knife orby other air separation devices, after which the heavy fraction isprovided to a rollback conveyor to remove the foam and round pieces. Atthis stage, two options exist. In a first option, the heavy fraction,which contains the wire and metals, is fed into one or more stages ofwire-metal separation, typically involving the use of one or morefloat/sink tanks as shown at 180 and 185, which yields as its output awire and metal concentrate. Although a single float/sink tank workswell, increasing volumes of throughput can be achieved by using multiplefloat/sink tanks.

In such an arrangement, the first float/sink tank can, for example, usewater as the media, which causes wood, rubber, and any remaining foam orlight rubber to float while the wire, metal and some other materialssinks. A second float/sink tank can involve a media with a higherspecific gravity, on the order of 1.4, which again causes the wire andmetals to sink but floats nearly all materials such as plastics, paper,and so on. The result is a wire concentrate, as shown at 190, as well asa residue of plastic and other materials that may be the subject offurther processing.

As a second option, shown at 195, the heavy fraction remaining afterstep 175 can be provided to a heavy media plant, which typically uses amedia including ferrosilicates to perform the metals separation. Withthis option, again, the result is a wire concentrate 190.

Referring next to FIGS. 2A-2C, a system which implements the processdescribed in FIG. 1 may be better appreciated. The system, indicatedgenerally at 200, is configured from multiple modules, each selected forinclusion in the system as appropriate for a specific material mix.Again, one typical material mix includes wood, rubber, metal, wire and avariety of types of polymeric, or plastic, pieces. These sorting modulescan include a magnetic separator portion 215, a rollback separator 220,a low pass dielectric module 225, shaker screening 230, a ballisticseparator 235, an inductive sensor sortation system 240, and a bandwidthdielectric module 245. The rollback separator 220 and the ballisticseparator 235 can also include an air knife or other air separationmodule 250. The air knife or air separation module can be implementedeither to move air upward or to move air downward, depending on theparticular implementation. One or more transfer conveyors 255, which maybe a friction conveyor or any other suitable conveyor, can beimplemented to move the stream of material mix from one module toanother. Likewise, a shaker feeder 260 may be implemented betweenmodules to evenly spread the material mix for processing by the nextmodule.

In general, the modules have the following functions, which may bebetter understood hereinafter in connection with the description ofFIGS. 3A-9B. The magnetic separator module 215 separates magneticmaterials in the material mix from non-magnetic materials. The rollbackseparator 20 separates round materials (e.g., foam, rubber and rocks)from irregularly shaped materials in the mix. The low pass dielectricsensor 225 separates less desirable wood, rubber and other materialsthat have a dielectric constant greater than a desired dielectricconstant from the valuable plastics. The low pass threshold or top ofthe range is typically on the order of 3.0 for an exemplary embodimentalthough a range of at least 3-5 has been found workable, depending onthe material and especially if the wood and other absorbent materialsare moist or wet. The shaker screen 230 separates small pieces such aswire, but may not be required in all embodiments, including particularlyembodiments which use an efficient air separation module 250. Theballistic separator 235 separates low surface area wire from highersurface area pieces such as shredded plastic on the basis of density andvelocity, although this function can alternatively be performed by afloat/sink tank where the media permits the wire to sink but causes theplastics and other materials to float.

In some embodiments, a separate inductive tensor sortation system 240separates wire and other non-ferrous metals from the wood, rubber andplastic portion of the mixed materials. The bandwidth dielectric sensor245 separates wood and rubber from remaining plastics within the desireddielectric range. Some or all of these sorting modules and other modulesdescribed in the applications incorporated by reference may be usedtogether to sort mixed materials. Again, for embodiments which permitthe wire to be effectively separated at an earlier stage, such anarrangement is not always required. Additionally, while this modulepermits wire to be effectively separated, the float/sink tankarrangement described hereinafter in connection with FIG. 10 canalternatively be used. In some embodiments, it may be desired to usemultiple float sink tanks, with media of different specific gravity toperform different sorting.

Each of the modules described above may be better appreciated from thefollowing discussion of FIGS. 3A-9B.

In a typical arrangement, the mixed materials to be sorted have beenshredded and screened in a manner known in the art so that theirphysical dimensions are preferably between 1″ and 5″. Multiple screeningsteps may be used to better remove dirt as well as other waste of smallsize, and the fraction removed by screening may be the subject offurther processing as desired. During the shredding process, the systemgenerates heat and causes much of the water that is normally in thewaste products to vaporize. If there is insufficient water in the mixedpieces being processed to sufficiently distinguish the material by knowndielectric const sorted by means of a mister or humidifier or otherconventional wetting device (not shown). The moisture from thehumidifier is absorbed by the dry wood, foam and other absorbentmaterials (raising the dielectric constant) but is not absorbed by theplastic materials (causing the dielectric constant to remain virtuallyunchanged). By making all of the wood, foam and other absorbentmaterials wet rather than dry, before the sorting process, the systemcan more easily distinguish the wood and other materials from theplastic pieces, thereby improving the accuracy of the sorting process.This can be particularly relevant to some embodiments of the sensorbeds, where maintenance of substantially constant temperature andhumidity can provide more uniform performance in at least someembodiments. The fact that the pieces are of substantially uniform sizealso permits more uniform operation. However, it will be appreciatedthat such temperature and humidity control is not required for allembodiments.

Although the stream of mixed recyclable materials to be sorted may besupplied by any of a variety of sources, one typical source is anautomobile/white good shredding line. These lines are well known in theart.

In an embodiment of the inventive system, installed in-line with theaforesaid automobile/white good nonferrous processing line, the mixedmaterials are first processed by the magnetic sorting module 215, shownin greater detail in FIGS. 3A-3B, which separates magnetic materialssuch as iron, steel and some ceramics from the mixed materials. Themixed materials, shown best in FIG. 3B, are placed on a moving conveyorbelt 310 traveling at a speed that can accommodate the full volume ofthe processing stream from the shredder line. The conveyor belt 310 canhave magnetic components 315 associated therewith or embedded thereinthat cause magnetic materials 320 in the mix to be attracted to theconveyor belt 310 through magnetic force. Alternatively, a magneticfield produced by permanent or electromagnets 325 can be generated atthe end of the conveyor belt 310 in a manner which causes the magneticpieces to be deflected by the magnetic field. As the conveyor belt 310rotates downward, the magnetic metal pieces are removed and fall into asegregated area 330. In an embodiment, a light air jet or air knife 250can be included to assist the magnet in deflecting lightly magneticpieces into the segregated area 330. The conveyor belt 310 can be seento be supported by a frame 335 and legs 340 in a conventional manner.While the magnetic sorting module is illustrated here as the firstmodule, and this order is appropriate in some embodiments, it will beappreciated by those skilled in the art that this order is not criticalin all embodiments, and in some embodiments (and for some types of mix)the magnetic module may be eliminated.

The non-magnetic pieces, or residue 345, are not affected by themagnetic field and pass through the magnetic sorting module to befurther sorted by subsequent modules. In an embodiment, and referringnow to FIGS. 4A-4B which illustrate the rollback separator module andadjacent elements of the overall system, the non-magnetic materialstravel across the adjustable feed conveyor belt, or assist frictionconveyor belt 255, that drops the materials onto the rollback separatormodule 220. The rollback separator module 220 separates rounded,comparatively heavy materials from comparatively flat or lightweightmaterials and comprises an adjustable pitch moving friction conveyor 410on which can be optionally disposed a plurality of bumps 415 to assistin retaining the desired portions of the mix. The pitch of the assistfriction conveyor 255 can be adjusted to control the height at the end420 where the material drops from the feed conveyor onto the rollbackseparator 220. Although the conveyor belt 410 is rotating upward asshown by the arrow indicating the direction of travel, relativelyrounded or heavy objects such as rocks and light, round objects such asfoam, indicated at 425, roll down against the direction of belt rotationand will fall into a segregated collection area 430. In contrast, flatpieces of materials, including, plastic, wire, rubber and wood willstick to the separator 220 and are transported off the upper end of theconveyor belt 410 onto the next module. It will again be appreciatedthat, while the rollback friction separator module is positioned secondin order in the illustrated embodiment, a different order may beappropriate in some embodiments or, depending on the mix and/or theimplementation, this module can be eliminated.

As noted previously, in some embodiments the textured surface of thefriction separator conveyor belt 410 can include a pattern of circularprotrusions or bumps 415 that provide friction. The protrusions can beon the order of about 1 mm high and ½ mm in diameter. The space betweenadjacent protrusions can be on the order of about ¼ mm. The rollbackseparator conveyor belt 410 can be fabricated of any suitably durablematerial which provides friction sufficient to grip the flat mixedpieces, and for example may be made of a variety of synthetic rubbermaterials. The angle and speed of the assist friction conveyor belt 255are adjustable so that the separation of materials can be fine-tuned toreduce errors in the subsequent modules including the dielectric sensorsortation module (i.e., round materials with low surface areas, such asrocks, if not consistently deflected by compressed air jets, and wetmaterials, such as foam, may give false dielectric readings). Similarly,the conveyor belt 410 can also be replaced with various belt materialsand texture surface patterns so that the friction coefficient of thebelt can be adjusted. More objects will tend to be passed through therollback separator 220 if the angle of the belt is low, the speed isslow and the friction coefficient of the belt is high. Conversely, ahigh angle, fast speed and smoother belt will pass fewer pieces but maycause of loss of some of the desirable materials. If desired, an airknife 250 can also be added near the top of the belt 410 to assist ininitiating the rolling off of the undesired materials. It will beappreciated that the rollback separator module is typically supported ona frame and legs similar to those shown for the magnetic separator 215.These elements are not shown in this instance for the sake of clarity.

The pieces of plastic, wire, metal, rubber and wood that adhere to therollback separator 220 are delivered to a shaker feeder 260. The shakerfeeder 260 has a substantially planar, smooth, inclined surface thatvibrates to evenly distribute the materials. The shaker feeder 260 maybe supported by a plurality of flexible or movable legs 435. A motor(not shown) is used to vibrate the substantially planar surface of theshaker feeder 260 that supports the flat pieces of plastic, rubber,metal and wood. The planar surface is preferably inclined so that thepieces fall off the lower end of the surface. It will be appreciatedthat, at this point, the residue of the mix primarily comprisesnon-magnetic and generally flat pieces, but still includes plastics,wire, wood, and so on.

Referring next to FIGS. 5A-5B, in one embodiment the non-magnetic andgenerally flat mixed materials are fed to a dielectric sensor sortationmodule 225, which can comprise multiple stages, arranged as a cascade inat least some embodiments, depending upon the particular material mixand the specific implementation. In an embodiment, the module caninclude a pan feeder 510 that vibrates to evenly spread the materialsonto either a conveyor belt, a slide or other platform which allows thematerials to pass over multi-stage dielectric sensor beds or arrays515A-B (two stages are shown for simplicity).

The dielectric sensor sortation module can comprise either digital oranalog dielectric sensors, or both. Although either type can be used inmost embodiments, it may be desirable in at least some instances toalter the type of sensor being used according to the composition of thewaste stream being sorted. As noted previously, it is generallypreferable to reject the minority fraction of a waste stream, and toallow the majority fraction to—continue forward. Thus, in an embodiment,digital dielectric sensors are used where the majority of the wastestream is recoverable plastics. In such an arrangement, the sensorthreshold is set for low pass operation, and the threshold is set forthe maximum dielectric of the acceptable material. Thus, the materialshaving a higher dielectric constant, typically wood and rubber and highdielectric plastics, are rejected, or diverted, for other processing. Onthe other hand, in an embodiment intended to sort a materials streamwhere the majority fraction is waste wood, rubber and high dielectricplastics, an analog sensor bed can be used. In such an arrangement, thesensor threshold is set to reject a range of dielectric constants whichencompasses all of the desired plastics. The plastics, which comprisethe minority fraction, are then rejected and redirected for furtherprocessing. In some embodiments, a combination of sensors may be used,or a bed having both types of sensors can be implemented, where only onetype of sensor is sensed for a particular stream of materials. It willbe appreciated that, while the foregoing discussion suggests the use ofanalog sensors for one arrangement and digital sensors for another, infact either type of sensor can be used for either low pass or high passoperation, and the choice is largely an implementation preference. Thus,for each example given herein, it will be appreciated that thecomplementary arrangements, both as to sensor and which materialsfraction is selected or diverted, are also possible and are notexplicitly disclosed for purposes of brevity.

To enhance the dielectric contrast of absorbent materials such as wood,paper, cardboard, carpet, and so on, these mixed materials may passthrough a humidifier 520 to moisten the exposed surfaces. In someinstances, the moisture content is excessive, and the materials can beflash dried with an IR heat source. As previously noted, maintenance ofa substantially constant temperature and humidity at this stage canprovide more uniform performance, and so in some embodiments thesestages of the separation system are enclosed by, for example,refrigeration plastic panels so that the interior area can be thermallyconditioned.

The low pass dielectric separation module 225 can include one or moreconveyor belts 525A-525B, as well as air jet arrays 530A-530B, wheretypically a conveyor belt is associated with each dielectric bed and atleast one air jet array is associated with each dielectric bed. Thedielectric sensor arrays 515A-B may be set to detect materials that havea dielectric constant greater than 3.0-5.0. As the mixed materialstravel over the first stage conveyor belt 151 they travel in closeproximity to the dielectric sensor array 515A that detects the materialsthat have a dielectric constant greater than the set value. When a highdielectric item is detected, a signal is transmitted to the associatedair jet array 530A which emits a blast of compressed air to deflect thetrajectory of the high dielectric material as it falls off the end ofthe first conveyor belt 525A onto a second conveyor belt 535 that takesthe diverted material away to a take-away conveyor 540 for secondaryprocessing. If the materials pass through the dielectric sensor array515A, and thus are assumed to have a low dielectric constant, they arenot deflected by the air jet array 156 and continue on through theseparation process.

In an optional arrangement, the materials that are not diverted by thefirst digital capacitive dielectric sensor array 154 are cascaded onto aconveyor belt 525B and transported over a second dielectric sensor array515B, to identify and select any materials that were missed by the firstarray. The dielectric settings of the first and second digitalcapacitive sensor arrays 515A-515B may be approximately equal or,alternatively, the second sensor array may be set to a differentdielectric threshold. For the example of a low pass array, materialsthat have a dielectric constant above the set point of the second sensorarray are deflected by a second air jet array 530B and diverted to thetake-away conveyor belt 540. The materials on the take-away conveyorbelt 540 may be transported for further processing as discussedelsewhere in this Specification. It will be appreciated that, while theforegoing description assumes that materials having a high dielectricconstant will be diverted from the main path for further processing asdesired, and low dielectric materials will continue, it is also possibleto reverse that process, such that materials having a low dielectricconstant are diverted for other processing, and those having a higherdielectric constant continue. Thus, which materials are processed whereis not a significant aspect of the invention; the objective is toprocess any of the materials that are desired for a particularimplementation.

Capacitive Proximity Sensors

The sorting process of the present invention includes a materialidentification step and a physical sorting step. In the past it has beenvery difficult to differentiate the rubber, wood and plastic because allhave very similar atomic numbers and specific gravities. It has beendiscovered that, when implemented properly, dielectric constant can beused to reliably distinguish these materials.

In the arrangement of the present invention, for example in the sensorarrays 515A-B, capacitive dielectric sensors are used to identify thedifferent material composition of each piece and to send a signal to asorting mechanism that separates the different materials along differentpaths. The dielectric constants for all materials ranges from about 1.0for materials such as air to 80.0 for water. Capacitive proximitysensors are good at detecting waste materials that have comparativelyhigh dielectric constants. For example, some known dielectric constantsfor common waste materials are listed below in Table 1.

TABLE 1 Poly- Poly- Poly- Dry Wet Material ethylene styrene propyleneWood Wood Rubber Dielectric 2.3 3.0 2.0-2.33 2-7 10-30 2.5-3.5 Constant

As illustrated above, the non-plastic materials tend to havesignificantly higher dielectric constants, especially when wet. It isinteresting to note that dry wood has a dielectric constant of 2-7, andrubber 2.5-35, and wet wood has a dielectric constant of 10-30. Byadding moisture to the absorbent materials, a dielectric sensor bed isable to separate out nearly all of the non-plastic materials exceptcertain rubbers having low dielectric constants. In addition,statistically, the vast majority of wood and rubber materials fallwithin a relatively narrow range of dielectric constants. For example,most rubber waste materials fall within a narrower range of 15-20. Thus,there is a distinct difference in the dielectric constant of plasticsversus wood and rubber. As a result, capacitive proximity sensors can beeffective at detecting materials within the mix that are not plastics.

Capacitive proximity sensors typically include a probe, an oscillator, arectifier filter and an output circuit. The capacitive proximity sensordetects the dielectric constant of the pieces passing nearby bygenerating an electrostatic field and detecting the changes in thisfield when the pieces pass by the face of the sensor. When a highdielectric piece is not detected, the oscillator is inactive, and when ahigh dielectric piece is detected, it can be diverted as discussed abovein connection with FIG. 5.

Different types of capacitive proximity detectors are available whichhave specific operating characteristics. In particular, shieldedcapacitive proximity detectors are best suited for sensing comparativelylow dielectric constant materials due to a more concentratedelectrostatic field. The electrostatic field of an unshielded capacitiveproximity detectors is less concentrated which makes them more suitablefor sensing comparatively high dielectric constant materials. However,for streams where the small particles and waste have been removed,unshielded dielectrics have proven adequate. Which dielectric sensor isappropriate will depend at least in part upon the particularimplementation and the waste stream to be processed.

Capacitive proximity sensors are also available with both digital andanalog outputs. While either type can be used in the present invention,depending upon the implementation, digital capacitive proximity sensorsoffer the ability to distinguish materials having dielectric valuesabove or below a set point, or threshold. For example, a digitalcapacitive sensor can distinguish materials above or below a dielectricconstant of 3.0 or other suitable set point. Most capacitive proximitysensors have a digital output that can be fed directly to a dataacquisition system of a computer. These digital capacitive sensors areused in the low pass dielectric separation module 225 in FIG. 2A.

In contrast, an analog capacitive proximity sensor can be used to detecta more narrow range of dielectric constants. For example, some analogcapacitive proximity sensors can detect materials that have a dielectricconstant between 2.5 to 3.0. These analog capacitive sensors are used inthe analog dielectric sensor module 245 shown in FIG. 2C. The analogcapacitive proximity sensors have an analog output which can span arange of output currents or voltages. In an embodiment, the analogoutput current may be 4-20 mA or the output voltage may be 0-10V. Thesecurrent or voltage signals are proportional to the dielectric constantof the material. The analog signals are processed by analog to digitalconverters and the digital signals are then fed to the data processingcomputer. Most stock capacitive proximity sensors are able to detect awide range of dielectric constants thereby distinguishing low dielectricplastic from high dielectric rubber. Although this wide range ofdielectric constants is useful for general sorting of mixed materials itis not as useful for sorting materials that have only small variationsin dielectric constants.

Because the inventive system can be used to distinguish materials havinga narrow range of dielectric constants, in some embodiments it may bedesirable to use capacitive proximity sensor having a limited detectionrange to more easily facilitate distinguishing materials having similardielectric constants. In other embodiments, the analog capacitiveproximity sensors may have an extended or amplified range of sensitivityover a narrower range of dielectric constants.

For systems built in accordance with the present invention that are usedto distinguish materials having modestly different dielectric constants,performance can, for some embodiments, be improved with capacitiveproximity sensors that have a high sensitivity. Although the sensitivityof a sensor is built into the device, it is also possible to alter andimprove the sensitivity based upon the housing and other factors. In anembodiment, the sensors are mounted into a machined piece of the slideor in a wear plate mounted under a conveyor belt. The sensors can, forexample, be placed in a counter-bored hole under the upper surface ofthe slide or wear plate. The sensitivity of the sensor may be altered bythe slide or wear plate material and its thickness, the diameter of thecounter bored hole and the depth of the hole. By adjusting thesevariables, the capacitive proximity sensors can be “tuned” for optimumperformance for the specific material detection application.

The operating frequency of the sensor corresponds to the detection timerequired to correctly detect the material selected for diversion, andthus affects operational speed. A faster operating frequency will beable to detect the selected objects more quickly than a detector with aslower operating frequency. The resolution corresponds to the size ofthe object being detected. A detector having a larger resolution is moresuitable for detecting large objects than a detector having a smallerresolution.

Although capacitive proximity detectors can detect the presence ofvarious types of wood and rubbers, this ability can vary depending uponthe sensor and the type of material being detected. The distinction insensitivity to specific types of wood and rubbers can be described invarious ways. One example of the variation in sensitivity based upon thetype of material being detected is the correction factor. Capacitiveproximity sensors typically have “correction factors” which quantifiesthe relative penetration distance for various materials. By knowing thebase penetration distance and the correction factor of the materialbeing detected, the penetration distance for any wood and rubber beingdetected can be determined.

In order to accurately detect the pieces of the selected material mixedin with other materials, the detectors must be placed in close proximityto determine the material of the piece being inspected. This can be doneby distributing the mixed pieces on a surface in a manner that thepieces are not stacked on top of each other and ensuring that there issome space between the pieces. The batch of mixed materials can be movedunder one or more detectors or alternatively the pieces can' be movedover the detector(s). The detection is based upon the size and materialof the wood and rubber.

The belts and slides used in the present invention can be made ofvarious materials. In some instances, it is desirable to selectmaterials for the belts and slides which have dielectric constantsoutside the range of the materials being detected, since, if thedielectric constant of the belt or slide is too close to the dielectricconstant material, the material can be harder to detect. For example, ifwood and rubber pieces—which have comparatively high dielectricconstants—are being detected, then a belt or slide of urethane, whichhas a very low dielectric constant, can be used since it outside therange of wood and rubber. However, detecting certain plastics with thisarrangement could be difficult since urethane has about the samedielectric constant as some of the plastics being sorted.

In a alternative arrangement, the conveyor belt or slide can, forexample, be made of a material that has a dielectric constant that isabout 7-8 which is between the lower dielectric constant plastics andthe higher rubber and wood values. In this embodiment the capacitiveproximity sensors will be able to easily detect the dielectric constantsof the plastic, wood and rubber pieces. This offers the benefit ofpermitting detection of even the different types of plastics, which mayhave different values in the marketplace.

The inventive system may be “tuned” in various ways for optimum resultsbased upon configuration of the sensors in the system. By altering thevariables associated with capacitive proximity sensors, the system canbe tuned to the particular application between performed. Thesevariables include: the depth and diameter of the mounting hole, thematerial used to mount the sensors and the type of capacitive proximitysensor being used. As one step, the tuning may be implemented by usingdifferent materials for the slide and/or conveyor belt, as discussedabove. The plate material used to mount the sensors can also alter thesensitivity of the capacitive proximity sensors. Also, differentpositions of the sensors in relation to the slide and/or conveyor beltwill influence the sensitivity and operation of the system. In anembodiment the mixed material pieces are placed on a moving conveyorbelt and the capacitive proximity sensors are mounted in a wear platethat contacts the lower surface of the conveyor belt. Thus, mixedmaterial pieces that are resting on the top of the conveyor belt areseparated from the wear plate by the thickness of the conveyor belt. Inan embodiment, the wear plate may be made of acrylic and the capacitiveproximity sensors are mounted in counter sunk holes in the acrylic. Thedepth of the capacitive proximity sensors may vary depending upon theirsensitivity. If sensors of different types or sensitivities are used ina particular sensor array, as may be desirable in some embodiments,different hole depths may be used for the different sensors.

The placement of the sensors away from the surface that supports themixed pieces will vary depending upon the range of the capacitiveproximity sensor and the desired operation of the system. It may bedesirable to have a sensor that has a range of 30 mm or more becausethis added range provides more resolution to differentiate the differentmaterials. Thus, a sensor with a longer range will be placed deeperunder the surface. With sensors of greater sensitivity, it is possibleto reliably differentiate between materials that have similar dielectricproperties, which can permit the system of the present invention todistinguish and separate different grades of similar materials such as:polyethylene, polystyrene and polypropylene which each have a slightlydifferent dielectric constant.

The sensitivity of the sensors can impact the accuracy of the sortingsystem in at least some embodiments, particularly where the materials tobe sorted include materials with very similar dielectric constants.However, more sensitive sensors typically are more expensive and may notbe required for a particular implementation. As a result, the designerof a particular system will typically match the sensitivity of thesensor to the relevant factors associated with the particular mix andthe materials used in the rest of the system.

Various methods may be used to improve the sensitivity of the capacitiveproximity sensors. As discussed above, in some embodiments it isdesirable to mount the capacitive proximity sensors in a slide or in awear plate under the conveyor belt. In addition, the mountingconfiguration itself can enhance the sensitivity of the capacitiveproximity sensors. As one example, if the capacitive proximity sensorsare mounted in a solid block of material that has a dielectric constantsimilar to the materials being sorted, it may enhance the detection ofmaterials that are directly above the hole in which the sensor ismounted, even though the dielectric constant of the mounting materialmay limit peripheral detection of materials. Depending on the design,the sensor may be mounted within a sleeve or tube fabricated for amaterial with a specific dielectric constant, and the assembly thenmounted in an appropriate location such as the wear plate. Sleeves ortubes of different dielectric constant materials can, in some instances,be selectively provided so that the material that produces the optimumsensitivity in the sensor can be used.

The geometry of the sensor holes may also affect the sensitivity of thecapacitive proximity sensors. A larger hole may require more material topass over in order to properly detect the dielectric constant, while asmaller hole may focus the electromagnetic detection and require lessmaterial volume to detect the dielectric constant.

The depth of the hole can also influence sensitivity, depending upon theother factors discussed above. In one embodiment, the system isconfigured to detect wood and rubber but not detect plastics. In thisembodiment, the hole may be deep enough to exceed the range of thesensor for plastic materials. Because the wood and rubber have a higherdielectric constant and produce a stronger detection signal, thecapacitive proximity sensors are still able to detect these materials.

In another embodiment, the system may be configured to detect anddistinguish plastics, woods and rubbers. In this embodiment, a lowsensitivity capacitive proximity sensor is mounted in a shallower holethan a high sensitivity capacitive proximity sensor to detect theplastic pieces. If different types of plastics are being sensed, acapacitive proximity sensor that has a very high sensitivity may berequired.

In some embodiments, it may be desirable to use sensors which arenarrowly tuned to a specific range, but which have improved ability todifferentiate materials with similar dielectric constants. For example,as specified in Table 1 above, polypropylene plastic has a dielectricconstant of 2.0-2.3, polyethylene has a dielectric constant of 2.3, andpolystyrene has a dielectric constant of 3.0. A sensor with appropriatesensitivity can distinguish polystyrene from polypropylene andpolyethylene to the extent the dielectric constants are different, forexample, to the extent they do not overlap. Multiple rows or arrays ofsensors can be used to add more precision.

An additional problem encountered with arrays of sensors as used in thepresent invention is crosstalk among the sensors. Cross talk is acondition in which detection signals intended to be detected by onesensor may affect other adjacent detectors. In general, the cross talksolutions discussed herein are applicable to the proximity sensorsmentioned herein for most embodiments. With reference to FIGS. 6A-6E,various configurations of sensor arrays having different crosstalk anddetection characteristics may be appreciated, with the objective ofpermitting a particular implementation to optimize the choice of arrayfor the needs of that implementation. As shown in FIG. 6A, a number ofdetectors 610 may be arranged in a linear one dimensional array across awidth of a slide or a conveyor belt 615 transporting the mixed materialpieces, typically plastics pieces 620 and wood and rubber pieces 625.This configuration allows the wood and rubber pieces 625 to be detectedby moving the mixed pieces across the row of detectors 610 whichsubstantially speeds the wood and rubber detection process. If aconveyor belt being used, it is, in at least some embodiments,substantially horizontal or only slightly inclined. Alternatively, aslide can be used, in which case the angle may be 35 to 70+ degreesdepending upon the types of materials being separated.

Because the typical detection range of the capacitive proximity sensorsis short, they are typically positioned comparatively close to eachother so that all wood and rubber pieces passing across the array ofsensors are detected; the exact dimensions will vary with the detectionrange of the specific sensor used in each particular implementation. Thesensors will preferably be arranged so that the wood and rubber pieceswill not be able to pass between the sensors and thus avoid beingdetected while at the same time not placing the sensors so closetogether that crosstalk becomes an issue.

There are various methods for avoiding or minimizing cross talk while atthe same time covering the entire width of the slide or conveyor belt.With reference to FIG. 6B particularly, the sensors 630 can be staggeredsuch that the sensors are not positioned close to each other yet anywood and rubber piece on the slide or conveyor belt will pass close toat least one sensor. When using a staggered configuration, the sensorsmay be setup in multiple rows of sensors 630. By having more rows ofsensors 630, the spacing between each sensor can be extended to avoidcross talk. In an embodiment, four or more staggered rows 635A-635D ofsensors 630 may be used. By placing these sensors 630 in four or morestaggered rows, the sensors are sufficiently spaced apart from eachother as to avoid any cross talk.

Another means for avoiding cross talk is by using sensors havingdifferent operating frequencies. Cross talk typically occurs onlybetween sensors operating at the same frequency. With reference to FIG.6C, by placing sensors operating at different frequencies next to eachother in the one dimensional array there is greater separation of samefrequency sensors, while at the same time permitting the sensors to bespaced more closely, if desired for a particular implementation. If twodifferent frequency sensors are used, an f1 detector 640 having a firstfrequency can be placed next to an f2 detector 645 having a secondfrequency. These detectors 640 and 645 can be arranged in an alternatingpattern, either in straight or staggered rows. Further, if sensors ofthird, fourth, etc., frequencies are used, additional separation can beprovided.

With reference to FIG. 6D, an arrangement can be seen which combinesalternating of frequencies and separation of the sensors into one ormore additional staggered rows of detectors. A first set of sensors 650operates at a first frequency, a second set of sensors 655 operates at asecond frequency, and a third set of sensors 660 operates at a thirdfrequency. By using different frequencies and/or using multiplestaggered rows of sensors, detectors 650, 655, 660 can be placed acrossthe entire width of the inspection area without causing significant, ifany, cross talk.

As discussed above, unshielded detectors can offer some advantages fordetecting large pieces while shielded detectors can offer someadvantages for detecting small pieces. Thus, the small and large woodand rubber pieces can be most efficiently sorted from the mixedmaterials by using both shielded and unshielded capacitive proximitysensors. With reference to FIG. 6E, a side view of an embodiment of theinventive sorting system is shown. In order to quickly and accuratelydetect all sizes of wood and rubber pieces, the mixed materials includeplastic pieces 620 and wood/rubber pieces 625. The mixed materials 620,625 pass in close proximity to at least one shielded sensor 665 and/orone unshielded sensor 670. As previously discussed, the conveyor beltshould be suitable durable for industrial applications, and ispreferably configured to permit the sensors to readily detect thematerials passing near the sensor array positioned either under thebelt, or above the belt, but without physical contact between thesensors and the material being sorted.

It will be appreciated by those skilled in the art that, at leastsometimes, the pieces being sorted can become deformed and twisted, inwhich case they may offer only a small profile for detection by thesensors. In addition, in at least some instances the undesirablematerials may be stacked above or below the desired materials, makingdetection more difficult. In such embodiments, an array of sensors bothabove the belt and below the belt can be used to improve the accuracy ofdetection. It will be appreciated that an upper array of sensors can bearranged in the same manner as the sensor bed below the belt, tominimize crosstalk and maximize detection. As discussed hereinafter,cascaded conveyors and multiple sensor arrays also assist in reducing“missed” materials, since the drop from one conveyor to another in thecascade is frequently sufficient to reposition a distorted or trappedpiece, making it easier for the sensors to identify.

The inventive materials sorting system can use shielded capacitiveproximity sensors 665, unshielded capacitive proximity sensors 670 or acombination of shielded and unshielded sensors 665, 670. In any of theseconfigurations, all signals from the detectors 665, 670 are fed to aprocessing computer (not shown). Because the shielded sensors 665 andthe unshielded sensors 670 are typically each better at identifyingspecific types of wood and rubber pieces 625, they may produce differentdetection signals for the same piece of wood, rubber or other material625. Because shielded sensors 665 are better at detecting small pieces,they will produce a stronger detection signal for, for example, smallwood and rubber pieces than an unshielded sensor 670. Similarly, theunshielded sensor 670 will produce a stronger detection signal for alarger pieces than the shielded sensor 665. In order to improve theaccuracy of the materials identification process, the processingcomputer can execute a program which prioritizes which type of signalwill be selected for a particular embodiment. For example the computercan execute an algorithm that uses the strongest detector signal toindicate the position of the detected piece 625. In this embodiment, themixed pieces 620, 625 can be passed by several rows of sensors 665, 670so that the selected pieces 625 are detected several times. The systemwill be more accurate because the position of the selected piece 625will be tracked by the detectors 665, 670 and the strongest detectionsignal will provide the most accurate position information. It will beappreciated that the computer includes a mechanism, for example alook-up table, which permits the program to correlate sensor locationwith position, so that the physical position of any detected materialcan be identified and tracked over time.

In an embodiment, the materials that pass through the low pass digitaldielectric sensor array(s) 515A-515B are transported preferably by atransfer conveyor belt 255 to the next module, best seen in FIGS. 2B and7. Initially, the material is passed to a shaker screen 230 thatseparates smaller sized pieces from larger materials. The shaker screen230 has a screen surface 710 that is vibrated by a motor and supportedby movable legs. The screen surface 710 includes an array ofperforations or holes to allow smaller pieces to fall through the screensurface. The shaker screen 710 can be slightly declined so that thematerial travels to one end and falls into separate segregated areas181. In one embodiment, the holes in the screen surface 171 can be onthe order of 18 mm in diameter, however the size of the holes istypically matched to the material being sorted and thus can vary over asignificant range. Larger holes will cause more pieces to fall throughthe shaker screen surface 171 and out of the continuing processing flow181. The small pieces may include dirt and the large pieces may includewire and low dielectric plastics. Alternatively, the sink/float tankdescribed in connection with FIG. 10 can be used to efficiently performthis separation function. When used for wire separation, the media ofthe float/sink tank may be water or water plus a compound to increasethe specific gravity, or a heavy media system, or a sand float system.

In an embodiment, the larger pieces sorted by the shaker screen 710 areplaced on a high speed ballistic conveyor belt 715 which separateslarger plastic materials from smaller pieces that were not separated bythe shaker screen 710. The high speed ballistic conveyor belt 715 isinclined upward and the materials on the high speed belt are acceleratedand projected off the end of the belt 715 as a function of theirdensity. For at least some embodiments, a belt speed on the order of 600feet per minute has been found suitable, although the speed can varywith the materials mix being sorted. In some implementations, an arrayof air jets 720 mounted at the end of the belt 715 is used to project aconstant low pressure stream of compressed air to help to separate thelower density materials out of the stream. The air jets 720 more readilydivert lower density materials than the higher density materials sincethe mass of lower density materials is less, where the material piecesare approximately the same size. Thus, the lower density materials suchas wire and dirt may be deflected to fall into a first segregated area725, while the greater momentum of the higher density materials such ashigh density plastics gives them a trajectory that allows them to beprojected farther away into a second segregated area 730.

There are various alternatives to the ballistic conveyor belt sortingmethod to separate plastic from wire. As one alternative, a specificgravity sorting method may be used. The specific gravity of plastic,wood, rubber and so on is typically about 1.4 while the specific gravityof wire and other metals is greater than about 2.5. If these pieces areplaced in a fluid material with a known specific gravity (such as water,sand or a heavy media) the plastic and other materials will be made tofloat while the wire and other metals will be made to sink. Such anarrangement is described in greater detail in connection with FIG. 10,and it will be appreciated that the float/sink tank of FIG. 10 can alsobe used to separate lighter and heavier plastic fractions, by adjustingthe specific gravity of the media. Other sorting methods that may beused include high definition metal detection, water bath and x-raydetection, as well as the heavy media system and sand float processdescribed earlier. At this point, it will be appreciated that thematerial mix has been separated into its key components, and highdensity, low dielectric constant plastic has been separated from allother materials to a relatively high degree of accuracy, typically wellabove 90% and in at least some implementations more on the order of 99%.This yields a commercially attractive recyclable product.

It is also possible to further sort the materials which were divertedbecause they had a higher dielectric constant than was desired in thelow pass sorting module 225, as briefly described in connection withFIG. 2C. With reference to FIGS. 8 and 9, these additional sorting stepsmay be better appreciated. In such an arrangement, the high dielectricmaterials that were separated by the lowpass dielectric sorting module225 can be transported by a conveyor belt 540 to a shaker feeder 810that is similar to the shaker feeder 260. The lower volume of highdielectric materials are fed by a conveyor belt which, in at least somearrangements, is permitted to travel at a slower speed than the originalfeed belt 310 and are the sorted by an bandwidth sensor module 240. Inat least some implementations, the bandwidth sensor module usesinductive sensors, the characteristics of which are discussed in greaterdetail hereinafter. The high dielectric materials pass by a highfrequency inductive proximity sensors array 810 that separate metalpieces from the non-metal pieces. When the metal pieces are detected, asignal is sent to an array of air jets 193 deflect the metal pieces intoa segregated area 195 by the use of software which maps and tracks thelocation of the items on the belt.

In some embodiments, a significant metal fraction may still remain. Forsuch embodiments, in the arrangement of FIG. 8, bandwidth sensor array240 detects non-ferrous metal pieces with inductive proximity detectors830 used in the inductive sensor array 810.

Different types of inductive proximity detectors are available whichhave specific operating characteristics. In particular shielded andunshielded inductive proximity detectors perform the same operation ofdetecting metal but have distinct operating characteristics which arelisted in Table 2.

TABLE 2 Shielded Inductive Unshielded Inductive Proximity DetectorProximity Detector Operating Frequency ~100 Hz ~300 Hz Resolution ~25 mmat 2.5 mps ~8.325 mm at 2.5 mps Penetration 40 mm 22 mm Diameter ~30 mm~30 mm Detection Time ~10 ms per cycle ~3.33 ms per cycle Belt Speed 0to 4 mps 0 to 4 mps

The operating frequency corresponds to the detection time and operatingspeed of the metal detection. A faster operating frequency will be ableto detect metal objects more quickly than a detector with a sloweroperating frequency. The resolution correlates with the size of theobject being detected. A detector having a larger resolution is moresuitable for detecting large metal objects than a detector having asmaller resolution. The penetration refers to the maximum thickness ofnon-metallic material that can cover the metal object that the detectorcan penetrate and still properly detecting the underlying metal such as,for example, insulated or coated wires and metals or stacked plastic andmetal pieces. A detector having a higher penetration depth will be ableto penetrate the non-metallic material and detect more metal pieces thana detector having a lower penetration depth. In at least somearrangements, unshielded inductive proximity detectors may be preferredfor detecting larger metal pieces while the shielded inductive proximitydetectors may be preferred for detecting smaller metal pieces.Embodiments using the sizing steps described previously will reduce theneed for such concerns in those arrangements.

The specifications in Table 1 are for typical 30 mm diameter inductiveproximity detectors. Changing the diameter results in changed operatingcharacteristics, and in particular, penetration distance can belengthened by enlarging the diameter of the sensor. The larger detectionarea can also result in slower detection time and may be moresusceptible to cross talk in some embodiments.

In addition to inductive proximity sensors that detect small and largepieces of metal, other inductive sensors offer somewhat differentcapabilities. For example, some coil based inductive proximity sensorsare able to accurately detect non-ferrous metals such as aluminum,brass, zinc, magnesium, titanium, and copper. Depending upon the metaldetection application, the material specific inductive proximitydetectors can be used with the other sensors to detect large and smallferrous metal pieces and non-ferrous metal pieces. The non-ferrous metaldetectors can be intermixed in the array of shielded and unshieldedsensors or added as additional rows of non-ferrous metal detectors tothe array, similar to the arrangements of capacitive sensors discussedpreviously. Although inductive proximity detectors can detect thepresence of various types of metals, this ability can vary dependingupon the sensor and the type of metal being detected in a manner knownin the sensing art.

As with the capacitive sensors discussed previously, the inductivesensors of the module 240 in order to accurately detect the metal piecesmixed in with the non-metallic pieces, the detectors must be placed inclose proximity to determine the material of the piece-being inspected.This can be done by moving one or more detectors over a batch of mixedmaterials or alternatively the pieces can be moved over the detector(s).

As discussed above, the unshielded sensors are slower than the shieldedsensors and require more time to accurately detect the metal pieces. Thedetectors can be configured with multiple rows of shielded sensors andfewer rows of unshielded sensors. By having additional rows of shieldedsensors, it is more likely that at least one of the several rows ofshielded sensors will detect the metal pieces.

Once the non-ferrous metals have been separated out from the mix by thebandwidth sorting module 240, the residue is passed through to an analogdielectric sensor module 245. As with the prior sensor arrays, an arrayof analog dielectric sensors 910 can be positioned above or below atransport belt, or both above and below, and can be programmed to detectmaterials within a range of dielectric constants, as discussedpreviously. The analog dielectric sensor sortation device 245 separateshigh dielectric wood and rubber materials from plastic materials. In anembodiment where the majority fraction of the materials stream is waste,the sensor array 910 uses a group of analog dielectric sensors that maybe set to a range of about 2.2 to 3.6 or other desired range. Whenmaterials are detected that have a dielectric value in the set range,such as the desired plastics which form the minority fraction of thestream, an air jet array 915 is actuated to reject the materials into afirst segregated area 920 and the remaining materials—with a dielectricvalue outside of the desired range—pass through the dielectric sensorsortation device into a second separate segregated area 925. Forexample, high dielectric plastics have a dielectric constant in therange of 3.0 to 3.8, while wood and rubber materials have a dielectricconstant above the 3.0 to 3.8 range, such that the analog sorting module245 permits an effective automatic sort of wood and rubber from thedesired plastics.

After the wood and rubber and plastic pieces are sorted, the sortedmaterials can be recycled. Although it is desirable to perfectly sortthe mixed materials, there will always be some errors in the sortingprocess. These errors can be due to the composition of the materialspassing over the sensor, the location of the pieces being stacked on topof each other, an insufficient separation of the pieces, moisture,sensor errors, etc. The analog sorting algorithm may be adjusted basedupon the strength of the analog detector signal output and environmentalvariables. An analog signal outside of the desired range is a strongindication of wood and rubber while a analog signal within the desiredrange is a strong indication of plastic. An algorithm sets a division ofwood and rubber pieces from the plastic pieces based upon signalstrength and can be adjusted, resulting in varying the sorting errors.The end user will be able to control the sorting point and may even usetrial and error or empirical result data to optimize the sorting of themixed materials.

Although the described sorting system for separating plastics from wood,rubber and other materials can have a very high accuracy of well over90%, it is possible to improve upon this performance. There are variousmethods for improving the purity of the majority and minority fractionsand accurately separating the wood and rubber from the plastics at anaccuracy rate close to 100%, one of which involves the use of cascadeddielectrics. The separation of the majority and minority fractionssorted as described above can be further purified by further sorting thematerials with a second primary sorting system and an additionalrecovery unit. The second primary unit and recovery units are bothsimilar to the first primary wood and rubber sorting processing unitdescribed above. The material sorted by the primary unit are placed ontoa second conveyor belt and passed close by additional arrays ofcapacitive proximity detectors in the second primary sorting unit. Thesesecond primary sort and recovery unit detector arrays can be configuredas described above: with mixed shielded and unshielded detectors,alternating operating frequencies for oscillator detectors, staggeredrows for coil and/or oscillator detectors and arrays mounted both overand under the surface of the conveyor belt. The waste or mixed materialfrom the second sort are forwarded to the recovery unit for a lastsorting process.

Like the first primary sorting unit, the outputs of the capacitiveproximity detectors in the second primary sort and recovery sort are fedto a computer which tracks the wood and rubber pieces. The computertransmits signals to the sorting mechanism to again separate the woodand rubber from the plastics. A high speed camera can be used with thesorting unit to more accurately detect the speed of the pieces. Lightsmay be necessary to improve the visible contrast of the pieces againstthe conveyor belt surface. Again, the wood and rubber pieces aredeflected into different bins at the end of the slide or conveyor belt.In the preferred embodiment, the sorting system used with the recoveryunit has air jets mounted under the upper surface of the slide orconveyor belt. The air jets are not actuated when the plastic piecesarrive at the end of the slide or conveyor belt and they fall into aplastics bin adjacent to the end of slide and the conveyor belt. Therecovery computer sends signals actuating the air jets when wood andrubber pieces arrive at the end of the slide and conveyor beltdeflecting them over a barrier into a wood and rubber bin. These undermounted air jets are preferred because the wood and rubber tends to beheavier and thus has more momentum to travel further to the wood andrubber bin than the lighter plastic pieces. The resulting accuracy ofthe pieces in the plastics bin of the recovery unit are up to 99+%.

It is estimated that a common yield from the described sorting processin an automobile and white good shredder recycling operation is 30-50%magnetic materials, 20-30% wood and rubber and 25-35% plastic and wire.The recovered magnetic materials may be pressed into pucks or briquettesthat may be recycled in a molten furnace process to produce carbon steelalloys. The recovered wood and rubber may be used as filler for cement,feedstock fuel or carbon additives for steel alloy.

Separation Mechanisms

The sorting system of the present invention can be used with some or allof the sorting modules described above with respect to FIG. 1. When thepieces to be sorted are detected, the computer synchronizes theactuation of the air jet with the time that the wood or rubber piecereaches the end of the plastic slide or conveyor belt. Alternatively, ahigh speed digital camera can be used to track the location of theobjects on the slide or conveyor belt and allow for accurate sorting. Byseparating the plastic and non-plastic pieces, the sorted plastic piecescan then be recycled. The plastic pieces may also be resorted toseparate the different types of plastics. Although the inventive woodand rubber sorting system has been described with an array of air jetsmounted over or under the slide or conveyor belt, it is contemplatedthat various other sorting mechanisms can be used. For example, an arrayof vacuum hoses may be positioned across the slide or conveyor belt andthe computer may actuate a specific vacuum tube as the wood and rubberpieces pass under the corresponding hose. Alternatively, robotic armswith suction, adhesive, grasping, a powered finger or sweepingmechanisms may be used to remove the wood and rubber pieces as they moveunder a sorting region of the system.

A further separation stage may be implemented in the manner shown inFIG. 10. FIG. 10 illustrates in cross-sectional side view a float/sinktank 1000, in which the media 1005 has a specific gravity which causescertain materials to sink, while other materials float. For example, aspreviously discussed, certain plastics float on water, while other sink.Thus, if water is used as the media, the float/sink tank 1000 canseparate lower density plastics and other residual materials from higherdensity plastics. However, in accordance with the present invention, thespecific gravity of the media 1005 may be selectively adjusted to permitseparation of other materials, for example copper wire, from lightermaterials such as plastics. For example, this approach also works forseparation of insulated copper wire from plastic pieces, even where suchinsulation is typically plastic, by adjusting the specific gravity ofthe media to approximately 1.4, although the specific gravity may behigher or lower depending on the desired sorting. If water is theprimary component of the media, the specific gravity of the media 1005may be adjusted by adding salt, magnesium sulphite, and calciumchloride, or other suitable materials. In some embodiments, calciumchloride is presently preferred for adjusting the specific gravity ofthe water-based media. In other instances, the media will be a dry sandprocess or a heavy media process, as discussed elsewhere herein (SeeFIG. 1B.) It will be appreciated by those skilled in the art that thepresent invention is not limited to either wet or dry process, nor anyparticular media, nor any specific material for adjusting the specificgravity of the media. It will also be appreciated that some embodimentswill include a plurality of float/sink tanks, each having a media of adifferent specific gravity, to better sort specific materials such asdifferent types of plastics. It is also possible to use a combination ofa float/sink tank with a heavy media process, or a sand float processfollowed by either a float/sink process or a heavy media process.

During operation of an embodiment, a stream of recyclable materials 1010is delivered to the float sink tank by any suitable means, for example aconveyor 1015 and a chute 1020. Where desired, the chute may have afairly steep angle to allow the materials in the stream 1010 to sinkpromptly upon entering the media 1005. Those with a specific gravityless than the media will thereafter resurface, while those with a higherspecific gravity will remain submerged. It will be appreciated that thechute 1020 is not necessary in all embodiments.

After the materials have separated in the media, the heavier materialswill be at the bottom of the tank, while the lighter materials will befloating at the top. It will be desirable in at least someimplementations to provide a mechanism for efficiently removing,separately, the two groups of materials. An example of such anarrangement is also shown in FIG. 10, wherein a drive mechanism 1030 ispositioned along the bottom of the tank to move the heavier materialstoward the proximal end of the tank, while a series of paddle wheels1040 are positioned along the length of the surface of the media to movethe lighter materials toward the distal end of the tank. It will beappreciated that the materials could be removed from either end, and thedecision of where the materials will be removed from the tank is merelyan implementation detail. The two separate groups of materials may thenbe removed by any suitable means. Suitable drive mechanisms for thebottom can include a drive screw with horizontally disposed slats orpaddles which substantially span the width of the tank, or can include adrag chain having the slats or paddles attached thereto, or can includea submerged conveyor. The bottom of the tank can be flat is a drag chainor submerged conveyor is used. If a screw drive is used, it can beuseful to provide a channel along the bottom of the tank into which thescrew can be placed. It will be appreciated that a curved outlet 1050may be provided for the removal of the surface material, where thepaddles are sized to substantially meet the curved outlet, while at thesame time having the chute long enough to permit the media to drain backinto the tank rather than being sloshed out of the tank. The specificmedia depends substantially upon the type of material being handled.

In an embodiment of the invention, it is possible to achieve a highlyefficient recovery of wire from the stream of recyclable materials,through the use of an initial magnetic separation to separate out theferrous materials, followed by an separation stage such as that shown inFIGS. 4A-4B to separate out a heavy fraction which typically includesrubber, wire and metals from a lighter fraction which typically includesplastics and foam. An air knife or other air system is typicallyimplemented in such an arrangement to assist in separating the heavyfraction from the plastics and foam. The heavy fraction can then beseparated into wire and rubber fractions by use of the float/sink tankdescribed in FIG. 10, where the wire typically comprises the heavyfraction. If the heavy fraction include dirt and fine particles, ascreening operation can be included prior to introducing the heavyfraction into the float/sink tank.

It will be understood that although the present invention has beendescribed with reference to particular embodiments, additions, deletionsand changes could be made to these embodiments, without departing fromthe scope of the present invention. Although a system has been describedthat includes very specific dielectric constant settings, it is wellunderstood that these settings and the described configuration ofsorting system units can be modified and rearranged in various otherconfigurations.

1. A plastic separation module, comprising: a specific gravityseparation module comprising a tank, the specific gravity separationmodule separating materials introduced into the tank according to apredetermined specific gravity; a first mechanism that removes floatingmaterials from a surface of the specific gravity separation module; anda second mechanism that removes sunken materials from a bottom of thespecific gravity separation module.
 2. The plastic separation module ofclaim 1, wherein the first mechanism comprises at least one paddlewheel.
 3. The plastic separation module of claim 1, wherein the firstmechanism comprises a conveyor having paddles thereon.
 4. The plasticseparation module of claim 1, wherein the first mechanism comprises awater jet.
 5. The plastic separation module of claim 1, wherein thesecond mechanism comprises a drag chain.
 6. The plastic separationmodule of claim 1, wherein the second mechanism comprises a submergedconveyor.
 7. The plastic separation module of claim 1, wherein thesecond mechanism comprises a screw drive.
 8. The plastic separationmodule of claim 1, wherein the specific gravity separation modulecomprises a float/sink tank.
 9. The plastic separation module of claim1, wherein the specific gravity separation module comprises a heavymedia system.
 10. The plastic separation module of claim 1, wherein thespecific gravity separation module comprises a sand float system. 11.The plastic separation module of claim 1, further comprising at leastanother specific gravity separation module, the specific gravityseparation modules containing media of a different specific gravity.